CPR is a process by which one or more rescuers may provide chest compressions and ventilation to a victim/patient who has suffered an adverse cardiac event—by popular terms, a heart attack. Chest compressions are considered to be the most important element of CPR during the first five to eight minutes after CPR efforts begin, because chest compressions help maintain circulation through the body and in the heart itself, which is the organ that can sustain the most damage from an adverse cardiac event. CPR may be performed by a team of one or more rescuers, particularly when the rescuers are professionals, such as emergency medical technicians (EMTs) on an ambulance crew. One rescuer can provide the chest compressions and another can time the ventilations of the patient to match the chest compressions according to appropriate CPR protocol. The CPR can be performed in conjunction with providing shocks to the patient with an external defibrillator, such as from an automatic external defibrillator (AED) that is designed to be used by laypeople. Such AEDs often provide audible information to rescuers, such as “push harder” (when the rescuer is not performing chest compressions forcefully enough), “stop CPR,” “stand back” (because a shock is about to be delivered), and the like.